but while running adb from command prompt i am getting error as "'adb' is not recognized as an internal or external command,operable program or batch file."
This is usually a path problem.
Linux
This is usually one of two problems on Linux.
First, adb is simply not on path. Its located in <Android SDK>/platform-tools, so platform-tools needs to be on path. To ensure its on path, you want something like this in your login script (.bashrc, .bash_profile, etc). Below is from Mac OS X and .bash_profile:
export JAVA_HOME=`/usr/libexec/java_home`
export ANDROID_NDK_ROOT=/opt/android-ndk-r9c
export ANDROID_SDK_ROOT=/opt/android-sdk-macosx
export PATH="$ANDROID_SDK_ROOT/tools/":"$ANDROID_SDK_ROOT/platform-tools/":"$PATH"
Second, the problem can occur on Linux if its x86_64 and you don't have ia32_libs installed. Tools like adb are 32-bit, so you need to install ia32_libs for the entire 32-bit subsystem for 64-bit Linuxes.
Windows
Windows has a PATH variable, and it can be adjusted per-user. Ensure <Android SDK>/platform-tools is on path in Windows. It would not hurt to ensure <Android SDK>/tools is on path also.

If you add a %PATH% variable, you can copy it from the System's %PATH% first. Then modify your copy.